Field of the Invention
The invention relates to a process and an apparatus for the open-loop control or closed-loop control of operating actions of at least one printing machine. The invention is applicable particularly in printing presses that contain devices for the handling, printing and treatment of sheets or other surfaces to be printed. Furthermore, the invention is applicable for the open-loop control or closed-loop control of devices that are positioned before or after a printing press, such as devices for the singling, folding, cutting, collecting, stacking, inserting, sorting and deposition of sheets or webs. Further areas of application are machines and devices for the bookbinding production and further treatment of printed products as well as devices for the inspection of printed products that permit, inter alia, the visual representation of the surface and/or a quality assessment of the printed products. The invention is used for the open-loop control and closed-loop control of operating actions that essentially influence the shaping and/or inking of a sheet, web or printed product.
The prior art comprises processes and apparatuses for the open-loop control and closed-loop control of operating actions on printing presses followed by cutting and folding devices. For the open-loop control and closed-loop control of inking and of the cutting and folding register, colored color-control strips, register crosses and other register marks--in addition to the actual printed image--are produced on the surface of the printing substrate as a sheet or a web is transported through the printing units.
For inking control, it is known, on the basis of color measurements in color fields of a specific color of the color-control strip, to obtain actual values for the inking control. It is also known, particularly in the case of decorative and special inks, to obtain actual values for inking control from image areas printed in full tones. Color measurement in the color fields or in the full-tone image areas may be carried out inside the printing press or off-line outside the printing press, for which purpose an inspection sheet is diverted out of the process and is supplied to a color-measuring arrangement. The preferably optoelectronically obtained measured color values may be passed on to an open-loop and closed-loop control circuit, where they are compared with setpoint values and are converted into manipulated variables for actuating elements of an ink-distribution apparatus.
Known for register adjustment are apparatuses that comprise on-line register-mark sensors which are directed at register marks that have been co-printed in register-mark tracks. Likewise, there are off-line apparatuses in which the register accuracy of register crosses is measured with a register-cross reader and the measured values are subsequently passed on to said printing-press control, where manipulated variables are generated for the register-adjusting devices.
A disadvantage of these solutions is that the measurement sites for determining the actual values of the operating variables to be controlled are fixed by the color-measurement fields, register crosses and register marks (which serve the purpose of quality control). The production of these measurement marks requires considerable effort at the pre-press stage.
The accuracy of such color-measurement fields and register crosses is limited by mounting, copying and developing errors at the pre-press stage. Furthermore, the color-control strips and register crosses, which are not part of the actual printed image, restrict the area available for the printed image on the printing substrate. The color-measurement fields of a color-control strip, which is usually positioned before or after the actual printed image as viewed in the transport direction of the printing substrate, are representative only to a limited extent of the printed image. The off-line color measurements delay the inking-control process, a quantity of waste being produced until an okay state is reached. Undefined instants of pulling, particularly when the printing press is not in a steady-state condition, lead to problems, such as overshooting in inking control. Furthermore, the existing solutions are inflexible with regard to the choice of the color-measurement site. The subject-dependent selection of the color-measurement site by the operator of the printing press is not provided for in the solutions according to the prior art. Furthermore, off-line color measurement means that the operator is involved over a lengthy period of time with the handling of the measurement objects and the color- and register-measuring apparatus. Consequently, the operator does not have at his disposal complete information on the trends with regard to inking and register adjustment.
Since separate actual-value-obtaining sensors must be provided for each of the various operating actions to be controlled, there is an increase in the effort and costs required for the open-loop control and closed-loop control of simultaneously more than two operating actions.